Camptothecin drug conjugate and use thereof

A drug conjugate of formula II or a pharmaceutically acceptable salt thereof,

• wherein
• Ab is an antibody or an antigen-binding fragment thereof,
• GT is a group connected to an antibody or an antigen-binding fragment thereof,
• GL is a single bond or a linking group;
• wherein GE is connected to GL;
• each GE is independently a polypeptide residue consisting of
• and t amino acid residues, each of the amino acid residues is independently a natural amino acid residue or a non-natural amino acid residue, and t is an integer of 1-10;
• Z1 and Z2 are independently —CH2— or O;
• GF and GS are a self-immolative group;
• G1 is
• each Rc is independently C1-6 alkyl;
• each Rc1 is independently
• each Rd is independently carboxyl,
• each Rd1 is independently H or C1-6 alkyl;
• m5 and m6 are each independently 1, 2, 3, 4, 5 or 6;
• Am is a single bond, a natural amino acid residue or a non-natural amino acid residue;
• D is
• X1 is NH or O;
• A is H, halogen, hydroxyl, amino, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C1-6 alkoxy, C6-10 aryl, 5- to 10-membered heteroaryl, C3-6 cycloalkyl or 3- to 6-membered heterocyclyl;
• RA, RB and RC are independently H, halogen, hydroxyl, amino, C1-6 alkyl, C2-6 alkenyl, C2-6 alkynyl, C1-6 alkoxy, C6-10 aryl, 5- to 10-membered heteroaryl, C3-6 cycloalkyl or 3- to 6-membered heterocyclyl;
• or, any two of RA, RB and RC together with the silicon atom to which they are attached form a C5-6 cycloalkyl ring or a 5- to 6-membered heterocyclyl ring, and the 5- to 6-membered heterocyclyl optionally further comprises one, two or three types of heteroatoms selected from N, O and S, and the number of the heteroatoms in the 5- to 6-membered heterocyclyl is independently 1, 2 or 3;
• X is O or S;
• n1 and n2 are independently 0, 1, 2 or 3;
• z is an integer or decimal of 1-16;
• 5- to 10-membered heteroaryl and 3- to 6-membered heterocyclyl each comprise one, two or three types of heteroatoms selected from N, O and S, and the number of the heteroatoms is independently 1, 2 or 3.